Extruded foam product with 134a and alcohol blowing agent

ABSTRACT

The present invention generally relates to methods for preparing extruded foam products and more particularly to a methods for producing such products with a blowing agent containing 134a and an alcohol.

FIELD OF THE INVENTION

The present invention generally relates to methods for preparingextruded foam products and more particularly to a methods for producingsuch products with a blowing agent containing 134a and an alcohol.

BACKGROUND OF THE INVENTION

Extruded synthetic resinous foams are useful materials for manyapplications including thermal insulation, decorative purposes,packaging and the like. Extruded foams are generally made by melting apolymer with any other additives to create a polymer melt, mixing ablowing agent with the polymer melt at an appropriate temperature andpressure to produce a mixture whereby the blowing agent becomes soluble,i.e. dissolves, in the polymer melt. This mixture may then be extrudedinto a zone of reduced pressure so that the blowing agent becomesinsoluble in the polymer melt and converts into a gas. As the blowingagent converts to a gas, bubbles are produced within the polymer melt.At this point, the polymer melt is cooled thereby producing a foamstructure comprising closed cells resulting from the expansion of theblowing agent.

Traditional blowing agents used for extruded foam manufacture includechlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). One ofthe advantages of CFC and HCFC blowing agents is their high solubilityin a polymer melt. Higher blowing agent solubility promotes viscosityreduction when mixed with the polymer melt. In turn, lower viscosityleads to lower energy requirements for mixing. A major disadvantage totraditional blowing agents is that an increasing number of governmentsworldwide have mandated the elimination of CFCs and HCFCs blowing agentsdue to growing environmental concerns.

Accordingly, there has been a movement to replace traditional blowingagents in favor of more environmentally friendly blowing agents such ashydrofluorocarbons. Unfortunately, hydrofluorocarbons (HFCs), and inparticular tetrafluoroethane (134a), have a lower solubility in polymermelts compared to traditional blowing agents. The present invention isdirected, in part, to increasing the solubility of 134a in a polymermelt by addition of an alcohol.

U.S. Pat. No. 5,182,308 issued to Volker et al. (“Volker”) discloses alaundry list of blowing agent compositions some of which include HFCsand alcohols. However, the blowing agent compositions of Volker produceextruded foams which have poor thermal insulating properties.Specifically, none of Volker's examples show extruded foams having acoefficient of thermal conductivity higher than 0.0376 W/mK as measuredby DIN 52 612.

Applicants have surprisingly discovered that by use of a blowing agentcontaining only 134a and alcohol, extruded foams may be produced withsuperior thermal insulating properties. The extruded foams made by thepresent invention have a coefficient of thermal conductivity lower than0.035 W/mK and preferably lower than 0.030 W/mK as measured by DIN 52612.

SUMMARY OF THE INVENTION

The present invention is directed to extruded foam products and theirmanufacture. The extruded foam products of the present invention have aplurality of closed cells containing a gas comprising 99% by volume of134a and have a coefficient of thermal conductivity lower than 0.035W/mK and preferably lower than 0.030 W/mK as measured by DIN 52 612. Theextruded foam products of the present invention are made with a blowingagent composition consisting of 134a and alcohol. The blowing agentcomposition preferably consists of 4-8 weight percent 134a and 2-5weight percent alcohol with the weight percentage based on the totalweight of the dry feed. The term “dry feed” used herein means all thematerials except the blowing agent which are used to make the polymermelt which is extruded. For example, the dry feed may comprise polymerpellets, nucleating agents, plasticizers, and any other ingredients toproduce the polymer melt.

DESCRIPTION OF PREFERRED EMBODIMENTS

Extruded Foam Manufacture Process

Although the blowing agent composition of the present invention may beincorporated in any process for making extruded foam products, thepreferred extruded foam manufacture process comprises heating, to afirst temperature, a resin mixture comprising a polymer to produce aplastified resin mixture; and thoroughly mixing a fluid blowing agentconsisting of 134a and an alcohol with the plastified resin mixtureunder a first pressure and under conditions preventing foaming of themixture. Once the blowing agent composition is incorporated andthoroughly mixed with the plastified resin mixture the resultingcombination is referred to as a foamable gel. The foamable gel is thencooled to a second temperature (generally referred to as die melttemperature), and is extruded into a zone of reduced pressure (secondpressure) resulting in foaming of the gel and formation of the desiredextruded foam product.

The first temperature must be sufficient to plastify or melt themixture. Preferably the first temperature is from 135-240° C., morepreferably is from 145-210° C., and most preferably from 150-165° C.Preferably the second temperature or die melt temperature is cooler thanthe first temperature. The die melt temperature is preferably from140-105° C., more preferably from 130-110° C., most preferably fromabout 125-115° C.

The first pressure must be sufficient to prevent prefoaming of thefoamable gel which contains the blowing agent. Prefoaming involves theundesirable premature foaming of the foamable gel before extrusion intoa region of reduced pressure. Accordingly, the first pressure variesdepending upon the identity and amount of blowing agent in the foamablegel. In one embodiment, the first pressure is from 700-4500 psia(4.826-31.02 MPa). In another embodiment, the first pressure is from840-4000 psia (5.791-27.57 MPa). In a preferred embodiment, the firstpressure is from 1150-3500 psia (7.928-27.57 MPa). In the most preferredembodiment, the first pressure is from 2200-3495 psia (15.16-24.1 MPa).

The second pressure is sufficient to induce conversion of the foamablegel into a foam body and may be above, at, or below atmosphericpressure. In one embodiment, the second pressure is from 0-28 psia(0-193 kPa). In another embodiment, the second pressure is from 1.4-21psia (9.652-144.7 kPa). In a preferred embodiment, the second pressureis from about 2.8-15 psia (19.30-103.4 kPa).

Polymer

Any polymer capable of being foamed may be used as the polymer in theresin mixture. The polymer may be thermoplastic or thermoset. Suitableplastics include polyolefins, polyvinylchloride, alkenyl aromaticpolymers, polycarbonates, polyetherimides, polyamides, polyesters,polyvinylidene chloride, polymethylmethacrylate, polyurethanes,polyisocyanurates, phenolics, copolymers and terpolymers of theforegoing, thermoplastic polymer blends, rubber modified polymers, andthe like. Suitable polyolefins include polyethylene and polypropylene,and ethylene copolymers.

A preferred thermoplastic polymer comprises an alkenyl aromatic polymermaterial. Suitable alkenyl aromatic polymer materials include alkenylaromatic homopolymers and copolymers of alkenyl aromatic compounds andcopolymerizable ethylenically unsaturated comonomers. The alkenylaromatic polymer material may further include minor proportions ofnon-alkenyl aromatic polymers. The alkenyl aromatic polymer material maybe comprised solely of one or more alkenyl aromatic homopolymers, one ormore alkenyl aromatic copolymers, a blend of one or more of each ofalkenyl aromatic homopolymers and copolymers, or blends of any of theforegoing with a non-alkenyl aromatic polymer. Regardless ofcomposition, the alkenyl aromatic polymer material comprises greaterthan 50 and preferably greater than 70 weight percent alkenyl aromaticmonomeric units. Most preferably, the alkenyl aromatic polymer materialis comprised entirely of alkenyl aromatic monomeric units.

Suitable alkenyl aromatic polymers include those derived from alkenylaromatic compounds such as styrene, alphamethylstyrene, ethylstyrene,vinyl benzene, vinyl toluene, chlorostyrene, and bromostyrene. Apreferred alkenyl aromatic polymer is polystyrene. Minor amounts ofmonoethylenically unsaturated compounds such as C₂-C₆ alkyl acids andesters, ionomeric derivatives, and C₂-C₆ dienes may be copolymerizedwith alkenyl aromatic compounds. Examples of copolymerizable compoundsinclude acrylic acid, methacrylic acid, ethacrylic acid, maleic acid,itaconic acid, acrylonitrile, maleic anhydride, methyl acrylate, ethylacrylate, isobutyl acrylate, n-butyl acrylate, methyl methacrylate,vinyl acetate and butadiene. Preferred structures comprise substantially(i.e., greater than 95 percent) and most preferably entirely ofpolystyrene.

The properties of the extruded foam product can be modified by selectionof the molecular weight of the polymer. For example, the preparation oflower density extruded foam products is facilitated by using lowermolecular weight polymers whereas the preparation of higher densityextruded foam products is facilitated by the use of higher molecularweight or higher viscosity resins.

Blowing Agent Composition

The blowing agent composition of the present invention consists of from4 to 8 percent by weight of 134a and from 2 to 5 weight percent of analcohol where the percent is based on the total weight of the dry feed.The alcohol may be chosen from C₁-C₅ alcohols and mixtures thereof.Examples of suitable alcohols include methanol, ethanol, propanol,isopropanol, tert-butanol, isobutanol, and mixtures thereof. Preferably,the alcohol is ethanol.

Optional Additives

Optional additives which may be incorporated in the extruded foammanufacture process include nucleating agents, infrared attenuatingagents, plasticizers, flame retardant chemicals, pigments, elastomers,extrusion aids, antioxidants, fillers, antistatic agents, UV absorbers,etc. These optional additives may be included in any amount to obtaindesired characteristics of the foamable gel or resultant extruded foamproducts. Preferably, optional additives are added to the resin mixturebut may be added in alternative ways to the extruded foam manufactureprocess. For example, optional additives may be incorporated before,during or after the polymerization process used to make the polymer inthe resin mixture.

Examples of nucleating agents useful in the invention include talc,calcium silicate, calcium carbonate, calcium stearate, clay, silica,titanium dioxide, barium sulfate, diatomaceous earth, indigo, etc. Inone embodiment, from about 0.01 to about 2 parts of nucleating agent per100 parts of the polymer are incorporated into the foamable gel. In apreferred embodiment, from about 0.05 to about 1 part of nucleatingagent per 100 parts of the polymer is incorporated into the foamablegel. Preferably, talc is added to the resin mixture as a nucleatingagent in the amount of from 0.1 to 5.0 wt. % based on the polymer,preferably from 0.1 to 1.0 wt. %, and most preferably from 0.4 to 0.6wt. %.

Plasticizers may also be added in the extruded foam manufacture process,preferably added to the foamable gel to facilitate processing of thefoamable gel in an extruder. In a preferred embodiment, the plasticizeris a low molecular weight resin (molecular weight below about 20,000).Examples of plasticizers include liquid paraffin or white oil,hydrogenated coconut oil, esters of C₄-C₂₀ monoalcohols, diols,glycerine with higher fatty acids, styrene resin, vinyl toluene resin,alpha-methylstyrene resin, etc. In one embodiment, from about 0.1 toabout 20 parts of plasticizer per 100 parts of the polymer isincorporated into the foamable gel. In a preferred embodiment, fromabout 1 to about 15 parts of plasticizer per 100 parts of the polymerare incorporated into the foamable gel.

Flame-retardant chemicals may also be added in the extruded foammanufacture process, preferably added to the foamable gel to impartflame retardant characteristics to the resulting extruded foam products.Flame-retardant chemicals include brominated aliphatic compounds such ashexabromocyclododecane and pentabromocyclohexane, brominated phenylethers, esters of tatrabromophthalic acid, and combinations thereof. Inone embodiment, from about 0.1 to about 5 parts of flame-retardantchemicals per 100 parts of the polymer is incorporated into the foamablegel. In a preferred embodiment, from about 0.5 to about 3 parts offlame-retardant chemicals per 100 parts of the polymer are incorporatedinto the foamable gel.

Extruded Foam Product Properties

The extruded foam products prepared in accordance with the invention arecharacterized generally as having the following characteristics.

The resultant extruded foam products generally have a relatively lowdensity, typically less than about 3 lbs/ft³ (48.0 kg/m³). Density canbe determined, for example, in accordance with ASTM D1622-88. In oneembodiment, the extruded foam products have a density from 0.1-3.75lbs/ft³ (1.60-60.0 kg/m³) In another embodiment, the extruded foamproducts have a density from 0.5-3.75 lbs/ft³ (8.00-60.0 kg/m³) In apreferred embodiment, the extruded foam products have a density from1-3.75 lbs/ft³ (16.0-60. kg/m³). In a more preferred embodiment, theextruded foam products have a density from 1.5-3.56 lbs/ft³ (24.0-57.0kg/m³).

The resultant extruded foam products generally have a relatively smallaverage cell size, typically less than about 0.4 mm. Average cell sizecan be determined, for example, according to ASTM D3576-77. In oneembodiment, the extruded foam products have an average cell size fromabout 0.01 to about 0.4 mm. In another embodiment, the extruded foamproducts have an average cell size from about 0.05 to about 0.35 mm. Ina preferred embodiment, the extruded foam products have an average cellsize from about 0.1 to about 0.3 mm. In a more preferred embodiment, theextruded foam products have an average cell size from about 0.15 toabout 0.25 mm.

The resultant extruded foam products generally have a relatively uniformaverage cell size, typically more than about 50% of the cells have asize within about 0.06 mm of the average cell size. In one embodiment,more than about 60% of the cells have a size within about 0.06 mm of theaverage cell size. In another embodiment, more than about 50% of thecells have a size within about 0.05 mm of the average cell size. In yetanother embodiment, more than about 50% of the cells have a size withinabout 0.045 mm of the average cell size.

The resultant extruded foam products generally contain a major amount ofclosed cells and a minor amount of open cells. The relative amount ofclosed cells can be determined, for example, according to ASTM D2856-A.In one embodiment, more than about 70% of the cells of the resultantextruded foam products are closed cells. In another embodiment, morethan about 80% of the cells of the resultant extruded foam products areclosed cells. In a preferred embodiment, more than about 90% of thecells of the resultant extruded foam products are closed cells. In amore preferred embodiment, more than about 95% of the cells of theresultant extruded foam products are closed cells.

In one embodiment, the resultant extruded foam products made inaccordance with the present invention have dimensional stability in anydirection of about 5% or less. In another embodiment, the resultantextruded foam products made in accordance with the present inventionhave dimensional stability in any direction of about 4% or less. In apreferred embodiment, the resultant extruded foam products made inaccordance with the present invention have dimensional stability in anydirection of about 3% or less. In a more preferred embodiment, theresultant extruded foam products made in accordance with the presentinvention have dimensional stability in any direction of about 2% orless as measured by ASTM D-2126/C578

The invention is illustrated with reference to the examples below. Inthe following examples density was measured in accordance with ASTM1622-88. Average cell size was measured in accordance with ASTMD3576-77. The coefficient of thermal conductivity was measured inaccordance with DIN 52 612.

EXAMPLE

Polystyrene was fed to a co-rotating twin screw extruder at a rate of160 kgs/hr, along with a flame retardant. Talc at 0.5 wt. %, based onthe weight of polystyrene, was added as a nucleating agent. The mixturewas melted in the extruder, which had been upgraded to provide moremixing, and mixed with 5.50 wt. % HFC 134a and 3.0 wt. % Ethanol basedon the total weight of the dry feed (i.e. talc and polystyrene). Theamps on the extruder were 58, the extruder discharge pressure was 218bar. The resulting gel was cooled, by an increased capacity coolingsystem, then foamed through a die to a region of lower pressure. Thepressure at the die was 90 bar. The foam panel produced had a density of2.85 lbs/ft³ (45.7 kg/m³), an average cell size of 0.2 mm, and acoefficient of thermal conductivity of 0.0271 W/mK.

Comparative Example 1

Polystyrene was fed to a co-rotating twin screw extruder at a rate of100 kgs/hr, along with a flame retardant. Talc at 0.5%, based on theweight of polystyrene, was added as a nucleating agent. The mixture wasmelted in the extruder, which had been upgraded to provide more mixing,and mixed with 11 wt. % HCFC 142b based on the total weight of the dryfeed (i.e. talc and polystyrene). The amps on the extruder were 42.8,the extruder discharge pressure was 234 bar. The resulting gel wascooled, by an increased capacity cooling system, then foamed through adie to a region of lower pressure. The pressure at the die was 53 bar.The foam panel produced had a density of 2.52 lbs/ft³ (40.4 Kg/m³), anaverage cell size of 0.25 mm, and a coefficient of thermal conductivityof 0.025 W/mK.

Comparative Example 2

Polystyrene was fed to a co-rotating twin screw extruder at a rate of160 kgs/hr, along with a flame retardant. Talc at 0.2%, based on theweight of polystyrene, was added as a nucleating agent. The mixture wasmelted in the extruder, which had been upgraded to provide more mixing,and mixed with 5.0 wt. % HFC 134a and 3.0 wt. % HFC 152a based on thetotal weight of the dry feed (i.e. talc and polystyrene). The amps onthe extruder were 67, the extruder discharge pressure was 233 bar. Theresulting gel was cooled, by an increased capacity cooling system, thenfoamed through a die to a region of lower pressure. The pressure at thedie was 91 bar. The foam panel produced had a density of 2.75 lbs/ft³(44.0 Kg/m³), an average cell size of 0.15 mm, and coefficient ofthermal conductivity of 0.0271 W/mK.

What is claimed is:
 1. A method for making extruded foam productscomprising: a) heating to a first temperature a resin mixture comprisingan alkenyl aromatic polymer and optional additives thereby producing aplastified resin mixture, b) thoroughly mixing with the resin mixture ablowing agent consisting of 134a 1,1,1,2-tetrafluoroethane and analcohol under a first pressure and under conditions to prevent foamingthereby producing a foamable gel, c) cooling the foamable gel to asecond temperature and extruding the formable gel into a second pressureless than the first pressure thereby causing the foaming of the gel andformation of an extruded foam product.
 2. The method of claim 1 whereinthe alcohol is a chosen from the group consisting of C₁-C₅ alcohols andmixtures thereof.
 3. The method of claim 1 wherein the alcohol is chosenfrom the group consisting of methanol, ethanol, propanol, isopropanol,tert-butanol, isobutanol, and mixtures thereof.
 4. The method of claim 1wherein the blowing agent consists of 4-8 wt. % 134a and 2-5 wt. %alcohol based on the total weight of the polymer and optional additives.5. The method of claim 1 wherein a talc is present as an optionaladditive.